1. Field of the Invention
This invention relates to a production method for a ceramic structure or a ceramic honeycomb structure. The method includes extrusion a ceramic material by use of a dedicated die. The invention particularly relates to an improvement of a extrusion rate during extrusion.
2. Description of the Related Art
A honeycomb structure assembled into an exhaust gas purification apparatus of an automobile, for example, is one of the structures produced from ceramics such as cordierite (refer, for example, to Japanese Unexamined Patent Publication (Kokai) No. 8-11528). This honeycomb structure includes a cylindrical outer cladding, partitions arranged in grid form inside the outer cladding and a large number of cells separated by partitions and penetrating in an axial direction.
To produce this ceramic honeycomb structure, a ceramic material containing ceramic powder, water, a binder and a lubricant is mixed and kneaded, extruded, and then dried and sintered.
In the honeycomb structure described above, it has been required to reduce the thickness of the partitions and the cell width in order to improve the performance of the exhaust gas purification apparatus. To satisfy this required, the slit width for forming the partitions must be reduced in the die used for extrusion.
However, the reduction of the slit width of the die for extrusion affects an extrusion step and eventually, productivity of an overall production process. In other words, when extrusion is conducted by use of an extruder using a die that has a reduced slit width, an extrusion pressure at the same extrusion rate is higher than when the slit width is great. Therefore, so long as the extruder having the same pressurization performance as that of existing extruders is employed, the extrusion rate unavoidably drops. The drop of this extrusion rate governs the overall production process of the honeycomb structure, and productivity drops.
The extrusion rate can be improved to a certain extent when a bigger extruder is used to increase the pressure. In this case, however, the temperature of the resulting molding rises and the shape of the extrusion cannot be retained. Therefore, a cooler for cooling the extruder must be added or the capacity of the cooler must be increased. As a result, the setup cost increases.
When the pressurization force is excessively increased, the die used for extrusion is broken, or extrusion defect occurs due to deflection of the die. Therefore, an increase in the pressurization force is limited.
For these reasons, development of a technology that can acquire a higher extrusion rate at a lower extrusion pressure than ever has been desired to extrude a honeycomb structure as the ceramic structure described above. In other words, when a extrusion pressure and a extrusion rate are plotted on the abscissa and the ordinate, respectively, and their relation is expressed by a graph, and when the gradient (rate/pressure) is defined as “extrusion rate efficiency”, development of a technology capable of increasing this extrusion rate coefficient has been desired.
If such a technology was available, the technology could be applied to the production of ceramic structures, having a sheet form and various other forms, besides the honeycomb structure described above.